Hydrogen is widely recognized as a renewable and clean energy source that has the potential to reduce dependence on fossil fuels. However, it is crucial to develop efficient, affordable, and sustainable electrocatalysts for hydrogen production through water splitting. To tackle this challenge, a bilayer Ni–Fe–Co-based sulfide was hydrothermally grown on Ni foam to boost the hydrogen evolution reaction (HER). SEM images revealed the micro-sized NiFe sheets decorated with NiCo nanosheets on the surface. The (NiFe/NiCo)S@NF electrocatalyst demonstrated outstanding performance towards HER in a 1 M KOH solution, where only a low overpotential of 185 mV vs. RHE was required at −10 mA/cm2, being considerably lower than those for NiFeS@NF (230 mV), NiCoS@NF (229 mV), NiFe@NF (237 mV) and NiCo@NF (256 mV) electrodes. This improvement could be attributed to the synergistic effect between constituents, the presence of Ni3S2 and NiCo2S4 phases, and the higher exposed area provided by the 3D nano/micro structure of the (NiFe/NiCo)S@NF electrocatalyst. Furthermore, this electrocatalyst exhibited the lowest Tafel slope of 76 mV/dec compared to NiFeS@NF (92 mV/dec), NiCoS@NF (87 mV/dec), NiFe@NF (89 mV/dec), and NiCo@NF (102 mV/dec), indicating its faster HER kinetics. Finally, in a two-electrode system of (NiFe/NiCo)S@NF||(NiFe/NiCo)S@NF, a low voltage of 1.58 V was required to obtain a current density of 10 mA/cm2 and the synthesized electrocatalyst had excellent stability over 12 h electrolysis. The achieved results proved that the (NiFe/NiCo)S electrocatalyst has great potential as a highly efficient electrode material for alkaline HER.
